The present invention generally relates to the detection of anomalies in elongate conductive members. The present invention is of particular importance in the context of detecting anomalies such as corrosion in pipelines. Anomalies can affect the function of the elongate conductive member. As an example, corrosion of steel pipes can degrade the structural integrity of the pipeline system.
The present invention will be described in the context of detecting corrosion in a steel pipeline, but the present invention has broader application to any elongate member capable of conducting electromagnetic signals having an anomaly that affects propagation of such electromagnetic signals.
In some pipeline systems, the metallic pipe is insulated with a urethane foam covering and protected by an outer metallic shield. This is often done to prevent heat loss. In other cases, the metallic pipe may be buried under the ground. For insulated, shielded, and/or buried pipes, visual inspection for corrosion on the outside of a shielded steel pipe is virtually impossible without physically removing the insulation and outer shield and/or excavating the pipe. For these insulated shielded pipes, visual inspection is impossible without physically removing the insulation and outer shield.
Corrosion can also occur within a pipe. Visual inspection of the interior of the pipe is also very difficult and is not practically possible when the pipeline is in use. One currently used method for pipeline inspection is to pass an instrumented probe, called a pig, through the entire length of the pipe and read out recorded data from the pig. Many pipelines cannot be tested this way because their construction does not allow passage of the pig.
Other methods of inspecting pipes include acoustic wave propagation through the metal, eddy current measurements, and x-ray radiography, but these methods are only applicable to a single point measurement or over a short distance. All but x-ray radiography require direct access to the surface of the pipe.
The assignee of the present application is also the assignee of a number of patents and published patent applications that disclose systems and methods for remotely testing conductive elongate members such as pipes. The systems and methods disclosed in these patents and patent applications can effectively determine the distance from a given measurement point to one or more anomalies based on time delay between the initial exciting pulse and the reflection from the anomaly. In particular, the systems and methods disclosed in the cited patents and patent applications employed only electric field probes. Using only electric field probes or sensors to time the wave arrival of the incident and reflected pulses at a single probe location allows the distance to, but not the direction of, anomalies to be determined by wave propagation calculation. Accordingly, these systems and methods are generally not effective at determining the direction of an anomaly on the conductive member relative to the measurement point.
The need thus exists for improved systems and methods for nondestructively testing for anomalies within a pipe structure.